1. Field of the Invention
This invention pertains to a process and composition for cementing (i.e. sealing or fixing) casing tubing into the borehole of a geothermal well. In the process, the novel slurries are used to fill the annulus between the casing and the wellbore and cured in place to form a tight seal between the casing and the formation and thus preventing communication between fluids in the different zones that the wellbore might traverse.
2. Prior Art
Furan polymers have very desirable chemical and physical properties which have made them the subject of considerable research. Furan polymers are normally obtained by the polymerization of furfuryl alcohol and/or furfural (furfuryl aldehyde). Normally the polymerization is heat activiated and acids are catalysts. The polymerization reaction tends to be very exothermic.
Goldstein et al, Ind. Eng. Chem., Vol. 52, No. 1, 57-58 (1960) described the polymerization of furfuryl alcohol in the presence of acidic catalyst. They identified zinc chloride as a preferred catalyst for this polymerization reaction and they also indicated that the catalyzed furfuryl alcohol solution had excellent storage life. The catalyzed solutions were used by Goldstein et al. to impregnate wood, brick, and carbon rods and the like to improve their chemical resistance and physical properties by the in situ formation of the furan polymer.
G. W. Anderson, World Oil, 37-43 (Feb. 1, 1978), used furfuryl alcohol as a one-step plugging agent in several shallow California oil wells which had been stimulated with steam. The furfuryl alcohol penetrated the matrix of these apparently incompetent formations and thermally cured after placement at the bottom hole temperature of 125.degree. F. The "plugged" interval in the formation prevented steam breaking through or channeling of steam around the uncemented casings.
There are various other references which show furfuryl alcohol used in down hole applications. For example: Burtch (U.S. Pat. No. 3,409,079) injected hot inert gases to cure furfuryl alcohol after placement to consolidate incompetent formations. Hess et al, Soc. Petroleum Eng. of AIME, S.P.E. Paper No. 3045 (Oct. 4, 1970) used furfuryl alcohol to plug thief zones in fluid (water, steam, gas) injection wells. They indicated that the material provided a strong durable plug at formation temperatures and had potential for reasonable durability under steam injection conditions where most plugging methods fail. In a later reference (U.S. Pat. No. 3,850,249), Hess described a method for treating a permeable formation or zone adjacent to the bore of an oil well by the injection and setting of an acid-setable liquid using a latent catalyst system. Examples of such acid-setable liquids included monomers such as furfuryl alcohol, furfural, etc., and condensates, such as urea-formaldehyde, phenol-formaldehyde, melamine-formaldehyde, furfuryl alcohol-formaldehyde, furfuryl alcohol-furfural, etc., and mixtures thereof. Hess also used a slurry of sand, furfuryl alcohol and a latent catalyst as a mortar to bond bricks.
Masek, Chem. Abst. 67: 67347v similarly added an acid-resistant, nonalkaline gravel to a catalyzed furfuryl alcohol/furfural system to make a "plastic cement." Other fillers have also been added to make furan polymer "cements." For example, carbon black was used by Maryla et al, Chem. Abst. 79: 79714y, to make a resinous cement in which the curable components were furfuryl alcohol and a phenol-formaldehyde condensate. Carbon black was also utilized by Lerch et al. (U.S. Pat. No. 2,349,181) as a filler in a pumpable liquid resin slurry; the curable components of which included a mixture of furfural and carbon disulfide, phenol, urea, thiourea, thiocresols, thiophenols, or derivatives of these compounds. These slurries were then used as a replacement for the heavier Portland cements to seal or fix casing tubes into a wellbore.
The weight of the cement is important in many instances because the formations are incompetent and this makes the heavy Portland cements difficult to use or inoperable in forming a tight seal. For example, Portland cements are generally unsatisfactory in cementing geothermal wells because such wells are generally produced in a fractured and/or incompetent formation.
Additional problems are encountered in cementing geothermal or geopressure wells because of the elevated temperatures encountered. The bottom hole static temperature (BHST) in such wells typically will range from about 300.degree. to 600.degree. F. A geothermal well is, of course, one which is drilled into a zone capable of producing hot water and/or steam. A geopressure well is one which is drilled into a zone having pressures considerably in excess of the hydrostatic pressure produced by a column of water at that depth. The hot fluids are produced from these formations by artesian forces. Geopressure wells normally do not have a problem of the formation being incompetent but do have the problem with elevated temperatures which adversely effect the properties of normal Portland cement.